The clearance between the cylinder and piston of an internal combustion engine needs to be maintained at least a minimum level in order to allow freedom of motion and to provide space for thermal expansion. This clearance is typically too high to provide an effective gas sealing. Thus, piston rings, typically in the form of pressure activated seals, are generally provided around the top of the piston to limit blowby of combustion products. Those familiar in the art recognize that a typical piston ring is split and its natural diameter is slightly larger than the cylinder in order to provide the pre-load when in place so that it naturally acts against the into cylinder wall.
The current invention improves the performance of piston rings in conventional internal combustion engines where a moving piston reciprocates within a fixed piston.
The invention also provides improved sealing on ported engines such as the Deckard engine where a cylinder rotates and reciprocates relative to a fixed piston.
The Deckard engine is an engine design that operates on the four-stroke cycle but with only one moving part. The Deckard engine is a very cost effective design for small applications where the four-stroke cycle is preferred over the two stroke.
Internal combustion engines are typically either two-stroke engines or four-stroke engines. For small engine applications such as model engines, chain saws, lawn trimmers, leaf blowers, and off road vehicles, two-stroke engines are often employed because of their lower weight, relative simplicity, lower cost, and high power to weight ratio relative to four-stroke engines.
Two-stroke engines, however, have inherently higher pollutant emissions than four-stroke engines because oil must be added to the fuel, and because the intake charge is incompletely burned. Another disadvantage of two-stroke engines is the relatively poor fuel efficiency, which results from this incomplete burning of fuel. Two-stroke engines are typically run "rich" which means that more fuel will be introduced than can be stoichiometrically combined with the oxygen provided. For instance, four-stroke engines will typically be run at air to fuel mass ratios of 13:1 to 15:1, while two-stroke engines may be run at a ratio of 10:1. Since this ratio is substantially below the stoichiometric ratio of about 14.8:1 for gasoline, it is impossible to burn all of the fuel introduced. The results of this incomplete combustion are reduced fuel economy and increased emissions.
From the consumer's perspective, the general advantages of four-stroke engines relative to two-stroke engines include: that there is no requirement to add oil to the fuel, that the smell is not as bad, that the engines are less noisy, that the engines are easier to start, that the engines provide better low-end torque, and that the engines run better at idle.
Four-stroke engines have improved emissions relative to two-stroke engines because they do not require the addition of oil to the fuel, and because they have more complete combustion. On the other hand, four-stroke engines typically require more moving parts than two-stroke engines.
For the foregoing reasons, there is a need for a simple, low cost, four-stroke engine. The preferred embodiment of this invention is a four-stroke ported internal combustion engine. The preferred embodiment provides a four-stroke engine with one major moving part, and few parts that require machining. In this embodiment, a cam means is used to link the rotation and translation of the cylinder relative to a generally fixed piston; and the rotation accomplishes the functions of a rotary valve, while the translation accomplishes the change of volume function. A transfer port, which is a recess in the cylinder wall, provides a path for intake of fuel and air through the intake port, as well as exhaust of combustion products through the exhaust port.
The preferred embodiment presented is a single cylinder, four-stroke internal combustion engine which comprises a cylindrical piston and a cylinder that rotates and reciprocates with respect to the piston. As the cylinder completes a revolution around the piston, a cam integral to the cylinder rotates through fixed cams and causes the cylinder to reciprocate through exhaust, intake, compression, and power strokes relative to the piston. These strokes correspond generally to the four-strokes of a conventional engine. A transfer port within the cylinder facilitates the intake of fuel and the exhaust of combustion products. The cylinder may include a cam and followers to control the cylinder movement.
Published past experimentation results establish that improving the secondary sealing can reduce hydrocarbon emissions. In those experiments, the conventional ring-pack of a spark ignition engine was replaced by a ring which was relatively wide in the direction parallel to the axis of symmetry of the piston ring, and that fitted relatively tightly on a similarly wide groove. The ring was pre-loaded by three round O-rings positioned one above the other. This prior art design has some disadvantages with respect to the current invention. The relatively tall ring which was at least twice the height of the of 1.5 to 2 mm conventional engines compression ring, will create a relatively large hydrodynamic drag. An objective of the current invention is to use a ring of approximate conventional height in order to minimize hydrodynamic drag. A second limitation of the prior art is that three O-rings and the tight piston-ring fit limits the pressure actuation of that design which is likely to compromise the sealing action at high loads and high cylinder pressures. Another objective of the current invention is to permit effective pressure activation of the rings.